Gaymar Industries, Inc., the assignee of this application, is a manufacturer of cushion like devices. These cushions which have at least one bladder are designed to contain fluids. In many cases the fluid is water and/or air. These cushions are used as seat cushions, mattresses, overlays and any other cushion designed to have a patient positioned thereon. Most of the cushions made by Gaymar are designed for therapeutic purposes.
Inflatable therapeutic cushions for patients have been known for many years. Many therapeutic cushions are designed to reduce “interface pressures”; the pressure encountered between a cushion and a patient's skin positioned on the cushion. It is known that interface pressures can significantly affect the well-being of immobile patients in that higher interface pressures can reduce local blood circulation, tending to cause bed sores and other complications. With inflatable cushions, such interface pressures depend (in part) on the air pressure within the inflatable support cushions.
In U.S. Pat. No. 5,794,289, Wortman et al. describe a cushion having a plurality of air cells (bladders). The cushion rotates a patient by controlling the air pressure in each air cell by inflation and deflation. To rotate a patient to its right side requires deflating the right air cells and inflating the left air cells. The air pressure required to rotate the patient depends on the patient's weight, body type and various other parameters.
The quantity of air pressure that rotates one patient, i.e., 30 degrees may rotate another patient, i.e., 5 degrees. For example, two female patients weigh 130 pounds, one patient is pear-shaped and the other is apple-shaped. The pear-shaped patient rotates 15 degrees with 10 mm Hg while an apple-shaped patient rotates 7 degrees with 10 mm Hg. Obviously each patient is unique and different. Therefore, the programming that controls the air pressure in each cushion must be altered to comply with each patient.
Programming an air pressure cushion unit requires a skilled technician. The skilled technician analyzes each patient and alters the programming to attain the desired air pressure. One method to avoid the expensive technician's analysis and re-programming is to create a self-monitoring mattress.
Previous self-monitoring air pressure cushions have utilized electrical signal transmission devices and electrical signal receiving devices. In one embodiment, the transmission device is a part of the top surface of a bladder and the receiving device is a part of the bottom surface of the bladder. That means the transmission and receiving devices are separated by a bladder cavity. By monitoring the duration of the signal from the transmitter to the receiver, the operator can monitor the size of the bladder. The size of the bladder corresponds to the air pressure and, if desired, the rotation of the patient. Such signal devices are disclosed in U.S. Pat. No. 5,794,289. Those signal devices generate electrical signals, like rf signals, that may, however, adversely effect other medical equipment. In particular, Wortman et al. disclose:
Referring to FIGS. 7 and 8, there is illustrated at 130 an inflatable cushion which is shown to be similar to cushion 44 but may be any other suitable inflatable cushion such as cushions 46 and 116. The cushion 130 is provided with button welds, illustrated at 132, to prevent ballooning thereof. The cushion 130 has upper and lower surfaces 134 and 136 respectively. Cushion inflation is related to the distance between the upper and lower surfaces.
In order to prevent bottoming-out from occurring and to more precisely regulate the cushion inflation, the cushion 130 is inflated so that the distance between the upper and lower surfaces is a predetermined distance. A transmitter coil 138 and a receiver coil 140 are provided adjacent the upper and lower surfaces 134 and 136 respectively, and the distance therebetween, illustrated at 142, is related to the signal strength of a signal transmitted therebetween. Alternatively, the coil 138 may be provided adjacent the lower surface 136, and the coil 140 provided adjacent the upper surface 134.
Illustrated at 141 in FIG. 10 is a transmitter for providing to coil 138 a signal which, as illustrated, may be a sinusoidal A.C. signal or may alternatively be a step-change or pulse signal. The received signal on coil 140 is amplified by a suitable amplifier 144, and the amplified signal sent to a suitable received signal strength indicator (RSSI), illustrated at 146, where a measure of signal strength is provided, in accordance with principles commonly known to those of ordinary skill in the art to which this invention pertains, which is suitably translated into a measure of distance 142 between the coils, which thus indicates whether the cushion is suitably inflated. A pair of resisters 148 are in series with the amplifier 144, and a resister 150 and diode 152 are in parallel with each other and with the amplifier 144. Illustrated at 160 is a suitably connector for lines to the coils 138 and 140. The coils and associated circuitry comprise what may be called an inductive loft sensor.
The RSSI 146 is suitably connected to a low height alarm, illustrated at 147, set for a predetermined low cushion height indicative of bottoming-out of the cushion due to low inflation pressure. The RSSI 146 is also suitably connected to a high height alarm, illustrated at 149, set to a predetermined high cushion height indicative of the patient being out-of-bed. A matrix or array of transmitting and receiving coil assemblies may be provided over the cushion area to provide position as well as height feedback.
In accordance with the present invention, the coils 138 and 140 are embedded within a flexible structure such as between thin plastic flexible sheets 154 and 156 which are suitably attached to each other such as by heat sealing. The sheets 154 and 156 may be said to comprise a generally rectangular blanket 158 with the coils 138 and 140 embedded in opposite halves of the blanket 158. The coils are spaced apart (in the plane of the unfolded blanket) a distance, illustrated at 131, equal to at least the maximum thickness of the inflated cushion 130. The blanket 158 is applied by folding it about the cushion so that one coil 138 is adjacent the upper surface 134 and the other coil 140 is adjacent the lower surface 136. Snaps, illustrated at 162, spaced along opposite terminal end edges of the blanket 158 or other suitable means are provided for suitably holding the blanket 158 in place on the cushion 130.
The system of the '289 patent does have some potential problems. One of those problems is that the transmission of the electrical signal may interfere with medical devices. Thus, there is a need to have a self-monitoring air volume cushion that monitors, without causing any possible adverse effect (transmitting rf transmissions) on other medical equipment, the bladder size to determine when to inflate a particular bladder to prevent bottoming and/or excess pressure.
An alternative, and for the most part non-transmitting self-monitoring air volume cushion device was disclosed in U.S. Pat. No. 6,145,142. In that patent (assigned to Gaymar Industries, Inc.), Rechin et al. disclosed a cushion having “at least one inflatable cushion having a pair of sides, and at least one set of an electromagnetic energy emitting device and an electromagnetic energy receiving device. The electromagnetic energy emitting device, when operating, illuminates the interior of the inflatable cushion. The electromagnetic energy receiving device collects the illuminating energy. The operation of the mattress requires a means for measuring the optical aperture of the inflatable cushion. The measuring means determines the optical aperture of the inflatable cushion by measuring the quantity of illuminating energy collected by the electromagnetic energy receiving device when the electromagnetic energy emitting device illuminates the interior of the inflatable cushion.” That device is interesting but it has never been incorporated into a publicly available cushion system made by Gaymar Industries, Inc.
In any case, both of those Gaymar patents illustrate that controlling the air in a cushion is desirable to prevent bottoming and prevent excess pressure being applied to the patient.
“Bottoming” refers to any state where the upper surface of any given cushion is depressed to a point that it contacts the lower surface, thereby markedly increasing the interface pressure where the two surfaces contact each other. Prior to bottoming occurring, the pressure exerted by the bladder on the skin of the object becomes excessive.
These bottoming sensors are acceptable but Gaymar has been seeking to improve such sensors. The improvements are made for numerous reasons. Some of these reasons are and not limited to cost (inexpensive), reliability, easy to install and adjust the system, and simplicity. In addition, the bottoming sensor should be able to diminish the chance of bottoming out and also decrease the chance that the cushion will exert too much pressure to the patient. All of these goals are accomplished with the present invention.